Six-stroke cycle engines have been proposed wherein the first four strokes function as a conventional internal combustion engine operating on a fuel charge and the fifth and sixth strokes operate on a steam charge. The fuel charge strokes include a standard intake stroke, a compression stroke, a power stroke, and an exhaust stroke. The products of combustion are exhausted from the combustion chamber, and water is injected therein to be converted by remaining heat into steam. The steam charge generates a steam expansion power stroke, and the steam is excised during a steam exhaust stroke.
Past attempts at such an arrangement have met with limited success, generally resulting in configurations of complicated construction and/or low efficiency. Examples include the engine described in U.S. Pat. No. 1,339,176, where the heat of the exhausted products of combustion were entirely lost, resulting in highly inefficient operation. Six-stroke cycle engines of the type shown in U.S. Pat. Nos. 1,217,788 and 2,671,311 relied on steam generating means external of the engine itself for providing the steam for a steam expansion stroke. Such arrangements were complicated and expensive to produce, and introduced additional components through which heat can be lost.
An engine described in U.S. Pat. No. 4,143,518 utilizes the reciprocating mechanism of the internal combustion engine for the steam power stroke and recovers a portion of the heat of the exhausted products of combustion. Such a configuration recovers only a small fraction of this exhausted heat. This is due to inadequate expansion during the steam power stroke and limitations on the maximum steam temperature that could be obtained by conducting the heat from the exhaust products through the cylinder walls. The heat of the exhausted products of combustion is recovered by passing the exhausted products over fins attached to the outside of the cylinder. The heat transferred to the fins is utilized to heat the cylinder wall. A primary limitation in this technique is that the cylinder wall can only be heated to approximately 400 degrees F. without destroying the oil film required to lubricate the piston. This significantly limits the maximum temperature of the steam formed when water is injected into the cylinder. In addition, no provision is made to adequately expand the steam. The expansion ratio of the fuel power stroke is limited to approximately 10:1 due to the characteristics of the gasoline used for a conventional internal combustion engine. This is insufficient for complete recovery of the mechanical work potentially recoverable from the steam during the steam expansion stroke.
The engine described by Hallstrom, U.S. Pat. No. 4,433,548, also utilized the reciprocating mechanism of the internal combustion engine for the steam power stroke. This design only recovers a small fraction of the exhausted heat due to limited expansion of the steam during the steam power stroke. The volume in which the steam is generated includes both the steam generation chamber and the clearance volume between the top of the piston and the cylinder head. No provision is made to minimize the clearance volume at the initiation of the steam power stroke. Therefore the steam expansion ratio is considerably less than the combustion cycle expansion ratio. This significantly limits the efficiency of the steam cycle.